The municipal public address (M.P.A.) system for disaster prevention is an important information facility in communities. The speech intelligibility of such a system, however, tends to be deteriorated by multi-path echoes with long time delay owing to reflections from nearby buildings and by the sounds from loudspeaker systems covering other subareas. When designing such an M.P.A. system, a tool effective for the prediction of outdoor sound propagation should be developed. For this aim, the authors have been investigating the applicability of a computer modeling technique based on geometrical acoustics. In addition, auralization is also desirable to assess the speech intelligibility of the M.P.A. system in acoustic design process. As a method for this purpose, the authors have been developing a simulation method in which the sounds calculated by the computer modeling are reproduced through a 6-channel reproduction system to realize spatial impression. As a result, it has been found that this simulation method is effective to investigate the sound propagation from an M.P.A. system with spatial information and can be used for auditory experiment to examine the speech intelligibility.
We developed a noise insulating material, which was made by molding bound small inorganic particles in inverse-L shape, to reduce the noise around an insulated rail joint in the continuous welded rail line. However, as the result of measurement made in a commercial line, it is revealed that its performance is insufficient due to its poor sound insulating and absorptive properties. Consequently, we have carried out its improvement in such a way as to promote its sound insulating properties by using aluminum plates as part of materials and its sound absorptive ones by using sound proof panels of 100 mm in thickness. Moreover, it has been decided to use two sorts of materials at the same time; one is a sound absorptive material for the railway track, the other is a rail insulating material for the general rail. As the result of measurement in another commercial line, it is found out that the materials have such sufficient performance as to reduce the noise level by about 3 dB around the rail joint.